With the ever increasing environmental consciousness of the world, the presence of trace organics in water, waste-water, and other effluents has also become increasingly important. Because many of these substances have toxic, carcinogenic, mutagenic and teratogenic properties, their presence, and particularly their concentrations, have increasingly become the focus of both environmental and health scrutiny. Particularly, the allowable concentration of a wide variety of potentially toxic compounds in waste-water is extremely low, as many have significant adverse effects and toxic activity, even when present in only trace levels of concentration (e.g., several parts per billion, or parts per trillion).
Continuing studies have been directed toward testing for, controlling, and determining permissible levels of a wide range of potentially toxic compounds, and much research has consequently gone into developing improved devices and procedures for testing for the presence of these various compounds. For example, the Environmental Protection Agency has adopted certain methods for the analysis of what have been named "priority pollutants" (as set forth in the Federal Register, Vol. 44, pp. 69,464 et seq. (1979)). Among these adopted methods are chromatographic techniques, combined gas chromatography and mass spectrometry techniques (GC/MS), and others. In addition to each of the various classes of compounds having their own specific analytical procedure for sampling, storing, collecting, and analyzing, it is widely understood in the industry that the EPA methods of analysis are labor intensive, equipment intensive, time consuming, and, as a result, costly. It is not unusual for an analysis of waste-water to take two days or more for result to be obtained. Many of these processes also require the collection of a relatively large sample volume (e.g., 1 liter), utilize relatively extensive amounts of laboratory glassware, tubing, and the like, require a relatively large volume of solvent for extraction and cleaning of the glassware and apparatus, and/or require significant energy input to evaporate the solvent and concentrate the sample compounds.
In general, compounds of interest have been extracted from waste-water for identification and quantification by passing a relatively large volume of the waste-water through a bed of granulated charcoal. U.S. Pat. No. 3,967,928 (Schmidt et al.) discusses a method of this type, wherein molecules are adsorbed on activated carbon product, followed by desorption. The compounds of interest are generally aborbed into the charcoal, after which a volume of extract (e.g., chloroform or the like) is passed through the bed of charcoal to release the adsorbed compounds. The extractant can be in the form of a solvent or a gas, and is generally chosen to release the compounds of interest from the charcoal bed. Thereafter, the extractant is evaporated to facilitate the assay of the concentrations and characteristics of the various compounds via a gas chromatograph (GC) device. While this particular procedure is widely utilized, because waste-water often contains particulate matter, the granular adsorbent can easily become plugged or otherwise clogged, thereby interfering with the reliability and efficiency of results obtained.
Other devices and methods for recovering compounds from waste solutions include the incorporation of a two-sided membrane, such as described in U.S. Pat. Nos. 4,525,278 (which issued to A. Frost) and 4,738,781 (which issued to W. Word et al.). Particularly, these references described ultrafiltration devices wherein waste-water or the like is fed through a tubular membrane of a non-cellulosic polymer through which compounds of interest permeate for removal through a separate output. Emulsified oils and suspended particles cannot pass through the membrane, and are removed as concentrated retente. The micro-porous membrane includes an exterior support tube which must also be porous in nature, such that it will have a low resistance to the permeating flow of the compounds of interest. Other references describing the use of two sided membranes for extraction of compounds of interest include U.S. Pat. Nos. 4,775,476 (Melcher et al.) and 4,819,478 (Melcher). While a two-sided membrane arrangement can be useful in certain circumstances, it is severely limited by the size and type of compounds which can permeate therethrough, must be isolated from pressure, and/or requires a porous supporting structure which must also be designed to allow penetration, and often requires relatively lengthy concentration times to allow for the permeation of the compounds completely through the membrane. Additionally, cleanup procedures are correspondingly difficult and time consuming, and potential carryover from previous test cycles can seriously undermine reliability of results.
Other methods for concentration of organics from aqueous solutions include the passage of the sample through an uncoated plastic or metal capillary tubing. For example, the procedures reported by Zlatkis et al. incorporated the use of relatively long capillaries (e.g., 50-100 feet) through which aqueous solutions were passed. The organic compounds would be retained in the tubing walls while the balance of the waste-water eluted from the capillary tubes. The concentrated organics were then desorbed from the capillary using an organic solvent, generally pushed through the capillary by nitrogen gas or the like. The desorbed solution was then analyzed by gas chromatography. Zlatkis et al. specifically set forth various problems with prior extraction techniques and devices, such as the charcoal filters discussed above. However, it was also reported that the effort to desorb the trapped organics were not satisfactory, and the use of metal capillaries was seriously questioned. Other methods for desorbing the organics, such as heating the matrix and/or utilizing a membrane dryer arrangement, were attempted to help remove the relatively large volumes of retained water required. Moreover, because long capillaries were needed, the cost, space and equipment requirements, and time for collection and analysis were clear negatives for the applicability and efficiency of these systems.
Consequently, there has heretofore not been available in the industry a relatively simple device and process for the extraction of particular compounds from sample solutions in a relatively reliable, efficient, and timely manner. Additionally, due to the permeable nature of two-sided membranes and their required porous supporting structures, as well as the cumbersome length of the capillary tubes utilized for GC analysis by Zlatkis et al., the methods and apparatuses previously available have not been easily adaptable to a variety of separation and assaying arrangements. A device and process having the higher sensitivity required for trace component analysis, while enabling smaller sample sizes and compatibility with water as both the sample and extractant carrier system and which can be used on-line with liquid chromatography and/or other separation/analyzing devices was needed. Moreover, the devices previously available were generally not easily used in conjunction with techniques requiring elevated temperatures and/or pressures.